Automotive air conditioning systems use a heat exchanger called a condenser that cools the compressed system refrigerant, and which experiences high pressures. To resist such pressures, it has been known for decades to use cylindrical tubes as the main structural component for the condenser, both for the flow tubes that carry the cooling refrigerant and for the manifolds that inlet flow to and outlet it from the flow tubes. This venerable design has come to be called a tube and fin condenser, and was a preferred design for a long time, both because of its structural simplicity and ability to easily withstand internal pressures of ten atmospheres or more. An improvement to this basic design, shown in co-assigned European Patent 0138435, involved the use of axially inserted plugs, sometimes referred to as separators or baffles, within the cylindrical manifolds to segregate the flow tubes into multiple passes. This improves thermal efficiency while leaving the manifolds uninterrupted at any point along their length, apart from the flow tube slots. Only the ends of the tanks, and the flow tube to tank interfaces, needed to be sealed. Such a design would be difficult to scale up to larger diameters, however, as it would be difficult to axially insert a larger diameter plug deep into a long cylinder without cocking or deformation.
While representing the simplest design, cylindrical tubes were not the most thermally efficient flow tube design, nor were cylindrical tanks the most spatially efficient manifold shape, despite their obvious high internal pressure resistance. Flat flow tubes were known to be more thermally efficient, since they present more surface area to be cooled for a given internal volume and, with suitable internal webbing, could be made sufficiently resistant to internal pressures. Flat tubes cannot be practically bent around into the hair pin shape often found in tube and fin condensers, however, so the manifold tanks are simply placed at opposite sides of the heat exchanger, as in a typical radiator. Likewise, manifold tanks with a rectangular cross section were known to be more space efficient, for the same reason that rectangular boxes stack more efficiently on a shelf than do cylindrical cans of a comparable size. Furthermore, by making such a rectangular cross section tank from a three sided extruded unit enclosed by a stamped and slotted tube header, and by providing sufficient material thickness and adequate brazing seams, enough internal pressure resistance could be provided. A two piece, brazed manifold assembly also provides the capability of stamping shallow separator grooves into the inner surfaces of the two pieces and accurately and easily inserting flow pass separators as the two pieces are assembled together. An example of such a condenser incorporating all of these features may be seen in co-assigned U.S. Pat. No. 5,062,476.
Despite the availability of rectangular tank designs with easy to install separators, designers have continued to work on designs that incorporate cylindrical (or nearly cylindrical) manifolds, while retaining the flat flow tubes, because of the inherently better pressure resistance (for a given material thickness and weight) that a cylindrical pressure vessel gives. Two design directions have been followed, one piece cylindrical tubes with plugged ends and two piece cylindrical manifold assemblies. One piece cylindrical manifolds simply scale up the diameter of a tube and fin condenser manifold, but face the difficulty of how to install the necessarily larger flow pass separators, as noted above. Since the larger flow pass separators cannot be simply axially rammed into place, they are typically inserted radially into the back of the tank through slots. An example may be seen in U.S. Pat. No. 4,825,941. This presents the real disadvantage of creating another potential leak path through the surface of the tank. Another problem is that the separator cannot be a simple circle, but must have a step in its outer edge in order be able to both seal against the inner surface of the tank and fill the slot in the back of the tank. Not being a simple circle, the separator has to be properly oriented during installation. A later design with a one piece cylindrical tank, U.S. Pat. No. 5,348,083, notes this deficiency, and does provide a separator that is a simple circle. However, the slot in the back of the tank must be more complex, including a pair of side barbs that are initially straight, and which are then bent in and around the circular separator after it is inserted. This adds an additional assembly step, and still represents a potential leak path.
Two piece cylindrical manifold assemblies, of which there are numerous examples, are basically the cylindrical structural equivalent of the two piece rectangular tank design noted above, with all the same inherent assembly advantages, but with the potential for greater pressure resistance for a given material thickness. Known two piece cylindrical tank designs have not, however, provided a simple separator or baffle design. U.S. Pat. No. 5,125,454 shows a separator that is not only very complex in shape, with numerous steps and notches, but which also, despite the two piece design, is inserted from the back through a separate slot, combining the worst features of one and two piece designs. U.S. Pat. No. 5,127,466 shows a two piece design in which one half cylinder slide fits down lengthwise into heavy, continuous internal flanges within the other half cylinder. While the design does not disclose separators per se, they would have to be of a notched or stepped design, as well, because of the internal discontinuity created by the extruded internal flanges. U.S. Pat. No. 5,036,914 shows a two piece manifold design with at least some embodiments that are free of internal discontinuities, though these embodiments do not have a circular cross section. Again, separators are not disclosed per se. The design intent for the separators can instead be seen in published European application EP-450-619-A, which has the same assignee, in FIGS. 8 and 9. The separators also have locating notches that pierce both the header and the tank. There appears to be a near consensus in the art, therefore, that separators in two piece cylindrical manifolds should have locating notches that pierce the wall of one or both pieces of the manifold. An exception is U.S. Pat. No. 5,341,872, which avoids separator locating notches by instead incorporating an additional component in the form of an internal locating rail that holds the separators. Besides the additional expense and bother of a separate component, the separators disclosed are still not simple circular disks, but also have notches that interfit with the locating rail, and which would require careful orientation at installation.